This invention relates to a semiconductor device using thick film resistors, a thick film resistor composition and a process for producing electroconductive particles for the thick film resistor.
Heretofore, RuO.sub.2 -based materials have been used as materials for the resistors in semiconductor devices such as thick film hybrid IC, etc., and Ag-Pd-based materials have been used for conductor circuits. These materials can be fired in air, but the Ag-Pd-based materials have a relatively high impedance, which has been a bottleneck in the needs for lower impedance in the semiconductor devices.
On the other hand, Cu-based circuit conductors have a lower impedance and a higher reliability than the Ag-Pd-based materials, and thus the Cu-based materials are used in some semiconductors such as hybrid IC, etc. However, Cu is readily oxidized and thus the firing can be only carried out in a non-oxidative atmosphere, for example, a N.sub.2 gas. In that case, the RuO.sub.2 -based materials as the resistor material are reduced to Ru in a N.sub.2 gas, and consequently lose the characteristics as the resistor. Thus, in semiconductor devices having Cu-based conductor circuits, a resistor composition comprising a metal boride, such as LaB.sub.6, glass powder and an organic vehicle is used as the resistor material, as disclosed in Japanese Patent Publication No. 59-51721.
However, these materials have such an inconvenience that no stable resistors having a sheet resistance of more than a few K.OMEGA./.quadrature. are obtained. Thus, as resistors susceptible to firing in a non-oxidative atmosphere, LaB.sub.6 -based materials are used for a low sheet resistance (10-5 K.OMEGA./.quadrature.) and SnO.sub.2 -based materials are used for a high sheet resistance (10k-1 M.OMEGA./.quadrature.).
As conductor materials for semiconductor devices such as thermal heads for video copying, etc., Au is used as a conductor material and RuO.sub.2 -glass-based exothermic resistors thermistors are used as resistor materials, as disclosed in Japanese Patent Publication No. 53-9543. These materials can be fired in air, but Au is a noble metal and Cu has been regarded as an electroconductive material as a substitute for Au.
Cu is a base material and thus must be fired in a non-oxidative atmosphere. When Cu is used as an electroconductive material, the thermistors for the thermal heads must be such that can be fired in a nonoxidative atmosphere. As the resistors that can be fired in the nonoxidative atmosphere, resistors based on a combination of LaB.sub.6 as an electroconductive component and glass are known, and it is possible to use these resistors as thermistors.
The so far proposed resistors have such a structure that LaB.sub.6 is dispersed in borosilicate glass, and generate a thermal stress due to the combination of different materials, when used as a thermistor for the thermal head, resulting in such inconveniences that a higher voltage is applied to the resistor and the change in the resistivity with time is increased.